Just changed cylinder head on a TD5, a few questions

So I've just changed the cylinder head on my TD5 and I've got a few questions before I fire it up.

1. My timing chain tensioner went in without much resistance. Does this mean it needs replacing or is it normal?

2. I've replaced the injector harness but now I can't get the plug to fully connect, it just jams up about 5mm from where it looks like it should finish. Can I put some WD40 or petroleum jelly on to loosen it up. I've checked and it looks like it's on the right way round.

3. While fishing through my oil pan to get my sump plug out I found what looks like a really large o-ring. Where's this from? Should I be worried?

Thanks, in advance.

Twinnie said:

3. While fishing through my oil pan to get my sump plug out I found what looks like a really large o-ring. Where's this from? Should I be worried?

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Too large to have passed through the sump drain hole perhaps? Probably already in the pan before you drained the oil

Thanks for the reply. I was lying in bed last night and realised it’s probably the one that was around the big plug over to timing chain sprocket.